1. Field of the Invention
The present invention relates to a substrate for use with a liquid jet recording head having an electro-thermal transducer and a transducer driving element such as a diode array or a transistor array arranged on one substrate, a liquid jet recording head having such a substrate, and a recorder having such a recording head.
2. Related Background Art
Many principles of discharging liquid have been known in a liquid jet recording method in which liquid is discharged to record data, and various forms of liquid jet recording heads and recorders which utilize such methods have been known.
Among others, a method for discharging liquid by utilizing thermal energy generated by an electro-thermal transducer is suitable for compact, extremely fine and elongated heads, and has been attracting attention.
In a known liquid jet recording head which uses the discharge method which utilizes the thermal energy, an electro-thermal transducer array is formed on a silicon substrate, a transducer driving functional element such as a diode array or a transistor array is arranged externally of the silicon substrate as a drive circuit for the electro-thermal transducer, and the electro-thermal transducer and the functional element are connected by a flexible cable or wire bonding.
In U.S. Pat. No. 4,429,321, a liquid jet recorder having the electro-thermal transducer and the functional element arranged on one substrate has been proposed in order to simplify a structure of the head, reduce trouble encountered during manufacturing process, unify characteristics of elements and improve reproducibility.
Where the method for discharging liquid by utilizing the thermal energy is adopted, a number of electro-thermal transducers are arranged to maximize the advantage thereof so that an elongated and high density head is attained. Where a number of electro-thermal transducers are used, a manner of wiring to the electro-thermal transducers is determined depending on a driving method therefor. In one known method, a common electrode connected in common to the electro-thermal transducers and individual electrodes individually connected to the respective electro-thermal transducers are used. In this method, in order to solve a problem of cross-talk in which one electro-thermal transducer is driven by the drive of another electro-thermal transducer, diodes for preventing the cross-talk are inserted between the respective individual electrodes or the respective electro-thermal transducers and the common electrode. However, since a current of several hundreds of milliamperes to several amperes flows through the common electrode depending on the number of commonly connected diodes, a surface area of the common electrode should be as large as possible. If the surface area is small, a voltage drop occurs due to a wiring resistance. If the voltage drop occurs during the drive of the liquid jet recording head, the discharge velocity of the liquid may be reduced, the diameter of the droplet may be reduced and the reproducibility of the operation may be lowered. This may be one of causes for disabling high grade and high quality recording.
If the surface area is too large and a number of electro-thermal transducers are arranged at a high density, the advantage of compactness which is attained by the use of the thermal energy may not be attained.
Further, the larger the surface area of the electrode is, the larger is the area of the crossing portion of the electrode. The crossing portion of the electrode is normally electrically isolated by an insulative layer except where electrical connection of the crossing electrodes is made. However, in most cases, since a defect such as dust or a pinhole exists in the insulative layer at a certain probability, there may be an area which has an insufficient insulative power. As a result, such an area causes shorting between the electrodes.
When the crossing area is large, a probability of a pinhole is high accordingly, and shorting is more likely to occur.
In order to avoid the above problems, it is preferable that an insulative film without defects be formed, but a total elimination of such defects is hard to attain and increases cost.
If the film thickness of the insulative film (insulative layer) between the electrodes is too thick, it will increase formation time. If it is too thin, the probability of defects of the film will increase. Accordingly, a proper thickness is desired.